Photographic film base subbed with acid-cooked pigskin gelatin



United States Patent G 7 3,1575% PHGTGGRAPl-EKI FILM BASE SUBBED WITH AGE-(ZQQKED PIGSKEN GELATlN .lohn W. Gates, (in, Paul E. Miller, Robert R. Phfilips, and Gale F. Nadeau, all of Rochester, N.Y., assignors to Eastman Kodak Qompany, Rochester, N.Y., a corporation of New Jersey No Drawing. (Eriginal application Nov. 8, 1957, Ser. No. 695,295, now Patent No. 2,992,213, dated .luly 11, 1951. Bivide-zl and this application Mar. 9, 1961, Ser. No. 94,431

Claims. (Cl. 95-457) This invention relates to the treatment of acid-cooked pigskin gelatin to adapt it to use for subbing photographic film base and the subbed film base and film obtained by its use.

This is a division of application Serial No. 695,205, filed November 8, 1957, which issued as US. Patent No. 2,992,213.

In the manufacture of photographic film the finished product ordinarily consists of a transparent film base of a polymeric material such as cellulose acetate, cellulose acetate propionate, polystyrene, polyester, or the like, containing a layer of silver halidegelatin photographic emulsion thereon. To fac litate good adherence of the emulsion layer to the film base, subbing layers are usually employed, of which gelatin is one of the important constituents. It is desirable that the gelatin employed have certain properties which make it suitable for this purpose. For instance, the gelatins usable as subbing materials in the preparation of photographic film bases should:

(1) Produce stable dispersions in the mixed solvents which are employed for applying the coatings thereto;

(2) Produce subbing layers which will not allow stripping otf of the emulsion layer either wet or dry and exhibit a high bonding strength to both the film base and the emulsion layer;

(3) Produce subbing lay rs having a high clarity and a minimum of color;

(4) Produce subbing layers with no wet haze. There are other properties of importance to this use such as photographic inertness to the emulsion layer applied thereon.

T he gelatins which are ordinarily employed for subbing purposes have been developed by long years of experience and trial and are generally prepared from limed cattle hides and calfskins and are of necessity of very low ash content so as to obtain good compatability and dispersion in the mixture of non-aqueous solvents which may be employed in applying the same to photographic film base.

The gelatins obtained from pigskins have been considered in this connection due to the generally high jelly strength of those gelatins. High jelly strength indicates that the gelatin has good adhesion to the film base. However, when deashed pigskin gelatins produced by means of the customary acid-cooked procedure or those from limed pigskins have been employed for photographic layers the light transmission of those gelatins has been poor and theircompatability with mixed solvents as employed for subbing has not been considered satisfactory. Therefore, even though gelatins having a jelly strength above 269 grains shoom are readily obtained from pigskin either by a' first run extraction or by a second run extraction thereof, nevertheless, those gelatins have shown properties which were not considered desirable for the purpose. Ordinarily in the obtaining of gelatin from pigskins, the acid-cook procedure is employed which involves the extraction of gelatin with water at a pH within the range of 45. After the grease has been removed from the extractant thus obtained, the resulting gelatin in aqueous solution can be made to gel by cooling giving products having a jelly strength above 260 shoom. It is to the use of those gelatins that the present invention is directed.

One object of our invention is to provide a procedure for treating pigskin gelatin to adapt it for use in subbing layers employed in the preparation of photographic films. Another object of our invention is to provide a gelatin from pigskin which will give layers when applied to transparent polymeric sheeting having a high bonding strength thereto, whether in wet or dry condition. A further object of our invention is to prepare from high jelly strength pigskin gelatin a product which possesses good light transmission properties and the capacity for giving smooth layers when coated out from its solution in mixed solvents onto a support therefor; other objects of our invention will appear herein.

We have found that acid-cooked pigskin gelatins of high jelly strength can be adapted to use for subbing purposes in the manufacture of photographic film if that gelatin is given an alkaline treatment within certain critical temperature and pH ranges. The treatment of the pigskin gelatin which should have a jelly strength of at least 269 grams shoom may be with either aqueous ammonia or with alkaline alkali metal compounds such as alkali metal hydroxide or alkali metal carbonate, for instance, sodium hydroxide, potassium hydroxide, sodium carbonate or the like. The treatment of the gelatin is carried out by leaching for a time such as 1-6 hours with the aqueous alkaline solution at a pH within the range of 895 and a temperature of 35-55 F. The length of time employed for this treatment may vary with the individual operator. The effectiveness of the treatment is the criterion of the length of time which one will wish to employ. We have found that a 4 hour treatment is ordinarily sulficient in every situation but if shortening of the time is desirable, in some cases the time used may be as little as 1 hour and a satisfactory product may be obtained. After the treatment of the gelatin with the alkaline liquor it may be employed directly for the subbing layers particularly following the ammonia treatment or it may be subjected before use to a deashing treatment with aqueous acetic acid as is well known in the art, the latter ordinarily being desirable where the treatment of the gelatin has been with alkaline alkali metal compound solutions. After the gelatin has been treated with the alkaline solution, it is washed'to remove water soluble salts or the like which might be present therein. This washing operation is carried out using several changes of cold water which may involve 3 or 4 or more washings of the gelatin. Although it appears that the use of distilled or demineralized water in the alkaline treatment or in the washing operation or both produces a better product than where tap water is employed, nevertheless, the use of tap water in these operations has been found to be efifective and its use is also included within the scope of the invention which we have made. To obtain gelatin of the best jelly strength, the first run type of gelatins may be employed but many second run gelatins have a jelly strength above 260 grams shoom and may be employed properties.

in the coating of subbing layers or in admixture with first run gelatin for that purpose. It has been noted that the acid which has been employed in preparing the pigskin gelatin may be any one of several acids; for instance, acids such as hydrochloric, sulfuric, acetic or the like may be employed and the extracted gelatins obtained will be substantially equivalent in characteristics.

The ammonia treatment of the gelatin may be carried out by lumping the gelatin such as in the form of flakes or noodles approximately 4 hours in cold water which has been adjusted to a pH of 8.5 with ammonia and following this treatment, the gelatin may then be subjected to successive treatments with cold water, each treatment being of approximately 4 hours duration. The

gelatin may then be melted if desired, and treated with acetic acid, or may be employed without such treatment;

In this treatment tap water may be used, particularly if.

the gelatin employed is a first run pigskin gelatin or a blend of first and second run gelatins in which the first run gelatin predominates. It is preferable when the gelatin treated is a second run gelatin that the water treatment be confined to the use of distilled water or demineralized water such as is obtained by the treatment of water with a zeolite or a permutit base exchange resin.

Instead of the ammonia treatment, the acid-cooked pigskin gelatin may be treated for 4 hours in cold water adjusted to a pH such as of 9 to 9.5 with sodium hydroxide. The gelatin can then be washed in water such as for 2 hours and deashed by treatment with changes of dilute aqueous acetic acid prepared with either dernineralized water or with tap water. This treatment is useful for'the treatment of either first run gelatin, second run gelatin or a mixture of first and second run gelatins extracted from acid-cooked pigskin providin of course, that the jelly strength of the gelatin is above 260 grams shoom.

The pigskin gelatins obtained by the alkaline treatments described are suitable for use in any of the accepted formulas for coating compositions for the application of subbing layers to film supports which compositions include gelatin therein. The layers thus obtained exhibit good light transmission properties and give smooth surfaces when coated out as subbing layers indicating the good compatability of the gelatin for the solvent mixtures which are employed in preparing the coating compositions.

The following examples illustrate the treatment of acid-cooked pigskin gelatins to render them useful for subbing purposes and typical subbing operations in which those gelatins have been used to give layers of good 1 Example 1 1 Two pounds of a second run acid-cooked pigskin gelatin was immersed in 20 liters of 0.1% sodium hydroxide solution having atemperature of 40-45 F. for 2 hours with occasional stirring. The liquid was drained from the gelatinand a second addition of 20 liters ofcold 0.1% sodium hydroxide solution was added to the gelatin and the mixture was stirred occasionally over a 2-hour period. The 0.1% sodium hydroxide solution had a pH within the range of 9-9.5. The liquid was drained from the gelatin and the gelatin was washed with distilled water with three one-hour changes. The gelatin was then deashed with aqueous acetic acid and dried in a current of warm dry air.

Pigskin gelatins which had not been ,deashe'd could not be tested for light transmission because those gelatins would not even disperse in the solvents employed for subbing procedure. The light transmission is determined by measuring the amount of light transmitted by sub solutions made with the various gelatins which values are all determined under the same conditions.

Example 2 l perature of 40 F, the pH of the water being adjusted to 8.5 with 28% aqueous ammonia. Over the time of treatment the pH was maintained at 8.5 by occasional ammonia additions. The water was then drained from the gelatin and the latter was washed with four 4-hour 20 liter leaches with cold water. Some of the gelatin was dried by means of a current of warm, dry air. The remainder of the gelatin was melted into solution, the pH thereof was adjusted to 4.65 with acetic acid and the mass was chilled and dried. The light transmission values of the gelatins thus obtained were found to be considerably improved over those of acid-cooked pigskin gelatins which had not been given an alkaline treatment in accordance with our invention. It was noted that when subbing layers of pigskin gelatin in accordance with our invention were applied to photographic film base, the pigskin gelatin layers were characterized by 100% resistance to stripping of the emulsion from the photographic Example 3 A batch of first run acid-cooked pigskin gelatin was treated with successive amounts of cold tap water sufficient in each treatment to thoroughly cover the gelatin. The gelatin which was in the form of flakes was stirred occasionally in each step. In the first step ammonia had been added to the water to hold the pH at 8.5 and the batch was stirred for 4 hours. The liquid was then removed therefrom and the gelatin was washed in 5 changes of water, stirring for 4 hours with each change. The gelatin flakes which resulted were dried 'under atmospheric conditions. The gelatin obtained had the characteristics which are desirable for a gelatin for employment for subbing purposes.

Example 4 A batch of first run acid-cooked pigskin gelatin in flake form was treated with several successive changes of cold demineralized water which water had a minimum of 500,000 ohms resistance. In the first two water treatments sufiicient sodium hydroxide had been added to hold the pH at 9.5 and the mass was stirred for 2 hours in each of the steps. After-removal of the alkaline treating liquid from the gelatin flakes, they were immersed in water and stirred for 3 hours. The water was re-' moved and the gelatin was subjected to 7 successive changes of water, in each case containing sufiicient acetic acid to reduce the pH to 45. In each of these treat: ments the mass was stirred for 1 hour. The gelatin flakes were then removed and were dried on nets in the air. The gelatin obtained was found to have good light transmission properties, gave good smooth surfaces when employed in the form of subbing layers, and thephotographic film prepared using this gelatin as at least one subbing layer exhibited high resistance to emulsion stripping.

The following examples are subbing compositions in which acid-cooked pigskin gelatinshave first been treated by procedures in accordance with our invention.

Example 5 useful for the coating of cellulose triacetate film support.

A. A subbing composition was prepared by dissolving 1.25% of deashed alkaline treated acid-cooked pigskin gelatin, 0.6% of sub type cellulose nitrate, 1% glacial acetic acid and 1.5% of the weight of the gelatin of chromic chloride in 60% acetone, 5% ethylene dichloride, 4% of water and the balance methyl alcohol to form 100% of subbing composition. A layer of this subbing composition was applied by the bead method to cellulose triacetate film support while it was maintained at a temperature of F. The sub coated support thus obtained was employed for preparing photographic film munby coating silver halide-gelatin photographic emulsion thereon. This emulsion layer when dried was found to be firmly bonded to the film support.

B. A photographic film support was prepared by coating cellulose triacetate film support with a subbing composition as described in A and there was then applied to this surface an overcoating layer of the following composition: 0.25% of deashed acid-cooked pigskin gelatin which had been treated in accordance with our invention, 0.25% of glacial acetic acid, 40% of methyl alcohol, 10% of butyl alcohol and 49.5% of water. The subbed film support was kept at a temperature of 150 F. and the overcoat solution was also heated to this temperature and applied to the sub layer under these conditions. The product obtained was coated with a silver halide-gelatin photographic emulsion layer and that layer was found to be firmly bonded to the film support.

Example 6 This example illustrates the use of acid-cooked pigskin gelatin treated as described herein for the preparation of compositions to apply subbing layers to film supports of cellulose acetate butyrate and cellulose acetate propionate.

A. A composition was prepared consisting of 1.25% acid-cooked pigskin gelatin treated as described herein, 3% of sub type cellulose nitrate, 1% of glacial acetic acid, chromic chloride in an amount 1.5% by Weight of the gelatin used, 50% acetone, 4% water and the balance methyl alcohol. The subbing layer was applied to a cellulose acetate butyrate film support by the bead ethod during which application the surface temperature of the support was maintained at 50 F. The resulting subbed film support was overcoated with a gelatin-silver halide emulsion which emulsion layer was found to be firmly bound to the cellulose acetate butyrate base.

B. Cellulose acetate butyrate support was coated as described in A and this subbed film support was then overcoated with an overcoating layer applied from a composition as described in B of the preceding example. To the subbed film base was applied on the subbed side a gelatin-silver halide photographic emulsion. The emulsion layer was found to be firmly bound to the film support.

Example 7 This example relates to the preparation of polystyrene film support for the application of photographic emulsion layer thereto by applying thereto at least one subbing layer containing pigskin gelatin treated in accordance with the invention.

To a polystyrene film support having a temperature of 75 F. was applied a layer using the following composition: 2.25% n-butyl methacrylate, 2.25% isobutyl methacrylate, 25% methyl alcohol, 25 n-butyl alcohol and 65.5% hexane. Over this subbing layer a layer was applied while the support was held at 75 F. of the following composition: 2.5% cellulose nitrate, 10% methyl Cellosolve, n-butyl alcohol, and 82.5% methyl alcohol. There was then applied to the film support at 100 F. over this layer a layer from a composition as follows: 1.2% acid-cooked pigskin gelatin which had been treated as described herein, 0.2% cellulose nitrate, 1.0% glacial acetic acid, chromic chloride in an amount 1.5% by weight of the gelatin, of methyl Cellosolve, of water and the balance methyl alcohol. Each of these layers was applied by the bead method and the subbing layers were each dried before application of the succeeding sub layer. There was then applied to the subbed polystyrene film support a gelatin-silver halide photographic emulsion. The emulsion layer thus applied was found to, be firmly bound to the polystyrene film support.

Example 8 There was applied to a polyethylene glycol terephthalate film support a layer of a resin latex consisting of a hydrosol obtained by polymerizing together 2 parts of itaconic acid, 15parts of methyl-acrylate and 82 parts of vinylidene chloride. After drying the coated film was stretched 200% in both a lengthwise and crosswise direction and was then crystallized by means of heat. The subbed polyester film support was then overcoated with a composition consisting of 0.5% acid-cooked pigskin gelatin which had been treated as described herein, 0.015% of a 10% solution of cetyl betaine, 0.017% of a 10% solution of chrome alum, 0.25% of urea and the balance water. The thus subbed polyester film support was heat cured for approximately 5 minutes at 250 F. There was then applied to the subbed polyester film support a layer of a photosensitive gelatin silver halide photographic emulsion. The emulsion layer was found to be firmly bound to the film support.

The firmness with which an emulsion layer is bound to film support is tested by a wet stripping test procedure in which the film is exposed to light and developed, fixed and washed as recommended for the photographic emulsion used. After washing the soft swollen emulsion is scored with a sharp pointed instrument and an attempt is thereupon made with the tips of the fingers to remove the emulsion from the film base by rubbing across the score marks. In addition an attempt is made to remove the emulsion from the cut edge of wet processed film by rubbing with the balls of the fingers. In the case of photographic films including the use of subbing layers containing acid-cooked pigskin gelatin which had been treated under the conditions of the invention described herein, the emulsion layers were found to be resistant to this Wet stripping procedure both when tested at the score marks and when tested at the cut edge of the sample.

Shoom is a jelly strength measurement of gelatin and is determined in the same manner as is Bloom except that the gelatin solution used has a concentration of 6.1% by weight of gelatin rather than the 6.6% conventionally used in determining Bloom by the Bloom gelometer. The Bloom gelometer and the determination of gelatin jelly strength therewith is described on Page 226 et seq. of Glue and Gelatin, J. Alexander (1923).

We claim:

1. A photographic film base containing thereon as a subbing layer a layer of acid-cooked pigskin gelatin which had been treated for 16 hours with an aqueous solution at 35-55 F. having a pH of 8-9.5 of a base selected from the group consisting of ammonia and the basic alkali metal compounds.

2. A photographic film base selected from the group consisting of film base of cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polystyrene and polyethylene glycol terephthalate containing thereon a subbing layer of acid-cooked pigskin gelatin which had been treated for 1-6 hours with an aqueous solution at 35-55 F. having a pH of 8-9.5 of a base selected from the group consisting of ammonia and the basic alkali metal compounds.

3. Cellulose triacetate film support containing thereon a subbing layer of acid-cooked pigskin gelatin which had been treated for 1-6 hours with an aqueous solution at 35-55 F. having a pH of 89.5 of a base selected from the group consisting of ammonia and the basic alkali metal compounds.

4. Cellulose acetate butyrate film support containing thereon a subbing layer of acid-cooked pigskin gelatin which had been treated for 1-6 hours with an aqueous References Cited in the file of this patent solution at 3555 F. having a pH Of 8-9.5 Of a base se- UNITED STATES PATENTS lected from the group consisting of ammonia and the 2 357 394 Frohlich et 31 Se t 5 1944 basic alkali metal compounds. 2398004 Houck et a1 i 1946 5. A photographic product comprising a photo 5 2 716 077 'Adarn et a1. Aug. 23 1955 film base, a subbing layer thereon of acid-cooked pigskin 2:823:12? Knox et a1 Feb. 1958 gelatin which had been treated for 16 hours with an 3,007,795 steigmann \NOV; 1961 aqueous solution at 35-55 F. of a base selected from the group consisting of ammonia and the basic alkali OTHER REFERENCES metal compounds having a pH of 8-9.5 and thereover a 10 Mees: The Theory of the Photographic Process, The gelatin-silver halide photographic emulsion layer. Macmillan Co., N.Y., 1942, page 60. 

5. A PHOTOGRAPHIC PRODUCT COMPRISING A PHOTOGRPAHIC FILM BASE, A SUBBING LAYER THEREON OF ACID-COOKED PIGSKIN GELATIN WHICH HAS BEEN TREATED FOR 1-6 HOURS WITH AN AQUEOUS SOLUTION AT 35-55*F. OF A BASE SELECTED FROM THE GROUP CONSISTING OF AMMONIA AND THE BASIC ALKALI METAL COMPOUNDS HAVING A PH OF 8-9.5 AAND THEREOVER A GELATIN-SILVER HALIDE PHOTOGRAPHIC EMULSION LAYER. 